#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

# define SWAP_LE32(x) (x)

typedef struct md5_ctx_t {
	uint8_t wbuffer[64]; /* always correctly aligned for uint64_t */
	void (*process_block)(struct md5_ctx_t*);
	uint64_t total64;    /* must be directly before hash[] */
	uint32_t hash[8];    /* 4 elements for md5, 5 for sha1, 8 for sha256 */
} md5_ctx_t;

/* Feed data through a temporary buffer.
 * The internal buffer remembers previous data until it has 64
 * bytes worth to pass on.
 */
static void c_hash(md5_ctx_t *ctx, const void *buffer, size_t len)
{
	unsigned bufpos = ctx->total64 & 63;

	ctx->total64 += len;

	while (1) {
		unsigned remaining = 64 - bufpos;
		if (remaining > len)
			remaining = len;
		/* Copy data into aligned buffer */
		memcpy(ctx->wbuffer + bufpos, buffer, remaining);
		len -= remaining;
		buffer = (const char *)buffer + remaining;
		bufpos += remaining;
		/* Clever way to do "if (bufpos != N) break; ... ; bufpos = 0;" */
		bufpos -= 64;
		if (bufpos != 0)
			break;
		/* Buffer is filled up, process it */
		ctx->process_block(ctx);
		/*bufpos = 0; - already is */
	}
}

# define FIX_ALIASING __attribute__((__may_alias__))
typedef uint64_t  bb__aliased_uint64_t FIX_ALIASING;

/* Process the remaining bytes in the buffer */
static void process_end(md5_ctx_t *ctx)
{
	unsigned bufpos = ctx->total64 & 63;
	/* Pad the buffer to the next 64-byte boundary with 0x80,0,0,0... */
	ctx->wbuffer[bufpos++] = 0x80;

	/* This loop iterates either once or twice, no more, no less */
	while (1) {
		unsigned remaining = 64 - bufpos;
		memset(ctx->wbuffer + bufpos, 0, remaining);
		/* Do we have enough space for the length count? */
		if (remaining >= 8) {
			/* Store the 64-bit counter of bits in the buffer */
			uint64_t t = ctx->total64 << 3;

			/* wbuffer is suitably aligned for this */
			*(bb__aliased_uint64_t *) (&ctx->wbuffer[64 - 8]) = t;
		}
		ctx->process_block(ctx);
		if (remaining >= 8)
			break;
		bufpos = 0;
	}
}

/*
 * Compute MD5 checksum of strings according to the
 * definition of MD5 in RFC 1321 from April 1992.
 *
 * Written by Ulrich Drepper <drepper@gnu.ai.mit.edu>, 1995.
 *
 * Copyright (C) 1995-1999 Free Software Foundation, Inc.
 * Copyright (C) 2001 Manuel Novoa III
 * Copyright (C) 2003 Glenn L. McGrath
 * Copyright (C) 2003 Erik Andersen
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */

/* 0: fastest, 3: smallest */
# define MD5_SMALL 0

/* These are the four functions used in the four steps of the MD5 algorithm
 * and defined in the RFC 1321.  The first function is a little bit optimized
 * (as found in Colin Plumbs public domain implementation).
 * #define FF(b, c, d) ((b & c) | (~b & d))
 */
#undef FF
#undef FG
#undef FH
#undef FI
#define FF(b, c, d) (d ^ (b & (c ^ d)))
#define FG(b, c, d) FF(d, b, c)
#define FH(b, c, d) (b ^ c ^ d)
#define FI(b, c, d) (c ^ (b | ~d))

static inline uint32_t rotl32(uint32_t x, uint32_t n)
{
	return (x << n) | (x >> (32 - n));
}

/* Hash a single block, 64 bytes long and 4-byte aligned */
static void im_process(md5_ctx_t *ctx)
{
#if MD5_SMALL > 0
	/* Before we start, one word to the strange constants.
	   They are defined in RFC 1321 as
	   T[i] = (int)(4294967296.0 * fabs(sin(i))), i=1..64
	 */
	static const uint32_t C_array[] = {
		/* round 1 */
		0xdf0269dc, 0xe245eb97, 0x15809a63, 0xcb099eed,
		0xf0e7dc1e, 0x3949467d, 0xb3007ee3, 0xfab76fcb,
		0x5bec6c09, 0x97623163, 0xff8261b2, 0x7cb8912e,
		0x78bc3989, 0xff302327, 0x9b05a966, 0x57aba0d5,
		/* round 2 */
		0xf9c25993, 0xb6387291, 0x34d9d288, 0xef54d603,
		0xcdc59078, 0x10f9378f, 0xe01d06a1, 0xe13456df,
		0x133e5b9d, 0xcc68e4f1, 0xf02133d0, 0x371354e9,
		0xb49d6648, 0xfa3fadca, 0x59ce1b77, 0x99347681,
		/* round 3 */
		0xff5beb9e, 0x7abcbc59, 0x7aba8747, 0xff5bbe12,
		0x99367a5a, 0x59cbc07d, 0xfa3f2610, 0xb49f2e97,
		0x3710e018, 0xf020549e, 0xcc6a6893, 0x133bd98b,
		0xe13324ad, 0xe01e3dd3, 0x10fbba08, 0xcdc41168,
		/* round 4 */
		0xef55ba8c, 0x34dc488c, 0xb636ae4c, 0xf9c2e6df,
		0x57adfdc9, 0x9b03a8fa, 0xff305662, 0x78be7151,
		0x7cb65edd, 0xff8239d5, 0x976438a1, 0x5bea1315,
		0xfab6eda3, 0xb3024b33, 0x3946d2ec, 0xf0e70246
	};
	static const char P_array[] = {
# if MD5_SMALL > 1
		0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, /* 1 */
# endif
		1, 6, 11, 0, 5, 10, 15, 4, 9, 14, 3, 8, 13, 2, 7, 12, /* 2 */
		5, 8, 11, 14, 1, 4, 7, 10, 13, 0, 3, 6, 9, 12, 15, 2, /* 3 */
		0, 7, 14, 5, 12, 3, 10, 1, 8, 15, 6, 13, 4, 11, 2, 9  /* 4 */
	};
#endif
	uint32_t *words = (void*) ctx->wbuffer;
	uint32_t A = ctx->hash[0];
	uint32_t B = ctx->hash[1];
	uint32_t C = ctx->hash[2];
	uint32_t D = ctx->hash[3];

#if MD5_SMALL >= 2  /* 2 or 3 */

	static const char S_array[] = {
		7, 12, 17, 22,
		5, 9, 14, 20,
		4, 11, 16, 23,
		6, 10, 15, 21
	};
	const uint32_t *pc;
	const char *pp;
	const char *ps;
	int i;
	uint32_t temp;

# if MD5_SMALL == 3
	pc = C_array;
	pp = P_array;
	ps = S_array - 4;

	for (i = 0; i < 64; i++) {
		if ((i & 0x0f) == 0)
			ps += 4;
		temp = A;
		switch (i >> 4) {
		case 0:
			temp += FF(B, C, D);
			break;
		case 1:
			temp += FG(B, C, D);
			break;
		case 2:
			temp += FH(B, C, D);
			break;
		case 3:
			temp += FI(B, C, D);
		}
		temp += words[(int) (*pp++)] + *pc++;
		temp = rotl32(temp, ps[i & 3]);
		temp += B;
		A = D;
		D = C;
		C = B;
		B = temp;
	}
# else  /* MD5_SMALL == 2 */
	pc = C_array;
	pp = P_array;
	ps = S_array;

	for (i = 0; i < 16; i++) {
		temp = A + FF(B, C, D) + words[(int) (*pp++)] + *pc++;
		temp = rotl32(temp, ps[i & 3]);
		temp += B;
		A = D;
		D = C;
		C = B;
		B = temp;
	}
	ps += 4;
	for (i = 0; i < 16; i++) {
		temp = A + FG(B, C, D) + words[(int) (*pp++)] + *pc++;
		temp = rotl32(temp, ps[i & 3]);
		temp += B;
		A = D;
		D = C;
		C = B;
		B = temp;
	}
	ps += 4;
	for (i = 0; i < 16; i++) {
		temp = A + FH(B, C, D) + words[(int) (*pp++)] + *pc++;
		temp = rotl32(temp, ps[i & 3]);
		temp += B;
		A = D;
		D = C;
		C = B;
		B = temp;
	}
	ps += 4;
	for (i = 0; i < 16; i++) {
		temp = A + FI(B, C, D) + words[(int) (*pp++)] + *pc++;
		temp = rotl32(temp, ps[i & 3]);
		temp += B;
		A = D;
		D = C;
		C = B;
		B = temp;
	}
# endif
	/* Add checksum to the starting values */
	ctx->hash[0] += A;
	ctx->hash[1] += B;
	ctx->hash[2] += C;
	ctx->hash[3] += D;

#else  /* MD5_SMALL == 0 or 1 */

	uint32_t A_save = A;
	uint32_t B_save = B;
	uint32_t C_save = C;
	uint32_t D_save = D;
# if MD5_SMALL == 1
	const uint32_t *pc;
	const char *pp;
	int i;
# endif

	/* First round: using the given function, the context and a constant
	   the next context is computed.  Because the algorithm's processing
	   unit is a 32-bit word and it is determined to work on words in
	   little endian byte order we perhaps have to change the byte order
	   before the computation.  To reduce the work for the next steps
	   we save swapped words in WORDS array.  */
# undef OP
# define OP(a, b, c, d, s, T) \
	do { \
		a += FF(b, c, d) + (*words) + T; \
		words++; \
		a = rotl32(a, s); \
		a += b; \
	} while (0)

	/* Round 1 */
# if MD5_SMALL == 1
	pc = C_array;
	for (i = 0; i < 4; i++) {
		OP(A, B, C, D, 7, *pc++);
		OP(D, A, B, C, 12, *pc++);
		OP(C, D, A, B, 17, *pc++);
		OP(B, C, D, A, 22, *pc++);
	}
# else
	OP(A, B, C, D, 7, 0xd76aa478);
	OP(D, A, B, C, 12, 0xe8c7b756);
	OP(C, D, A, B, 17, 0x242070db);
	OP(B, C, D, A, 22, 0xc1bdceee);
	OP(A, B, C, D, 7, 0xf57c0faf);
	OP(D, A, B, C, 12, 0x4787c62a);
	OP(C, D, A, B, 17, 0xa8304613);
	OP(B, C, D, A, 22, 0xfd469501);
	OP(A, B, C, D, 7, 0x698098d8);
	OP(D, A, B, C, 12, 0x8b44f7af);
	OP(C, D, A, B, 17, 0xffff5bb1);
	OP(B, C, D, A, 22, 0x895cd7be);
	OP(A, B, C, D, 7, 0x6b901122);
	OP(D, A, B, C, 12, 0xfd987193);
	OP(C, D, A, B, 17, 0xa679438e);
	OP(B, C, D, A, 22, 0x49b40821);
# endif
	words -= 16;

	/* For the second to fourth round we have the possibly swapped words
	   in WORDS.  Redefine the macro to take an additional first
	   argument specifying the function to use.  */
# undef OP
# define OP(f, a, b, c, d, k, s, T) \
	do { \
		a += f(b, c, d) + words[k] + T; \
		a = rotl32(a, s); \
		a += b; \
	} while (0)

	/* Round 2 */
# if MD5_SMALL == 1
	pp = P_array;
	for (i = 0; i < 4; i++) {
		OP(FG, A, B, C, D, (int) (*pp++), 5, *pc++);
		OP(FG, D, A, B, C, (int) (*pp++), 9, *pc++);
		OP(FG, C, D, A, B, (int) (*pp++), 14, *pc++);
		OP(FG, B, C, D, A, (int) (*pp++), 20, *pc++);
	}
# else
	OP(FG, A, B, C, D, 1, 5, 0xf61e2562);
	OP(FG, D, A, B, C, 6, 9, 0xc040b340);
	OP(FG, C, D, A, B, 11, 14, 0x265e5a51);
	OP(FG, B, C, D, A, 0, 20, 0xe9b6c7aa);
	OP(FG, A, B, C, D, 5, 5, 0xd62f105d);
	OP(FG, D, A, B, C, 10, 9, 0x02441453);
	OP(FG, C, D, A, B, 15, 14, 0xd8a1e681);
	OP(FG, B, C, D, A, 4, 20, 0xe7d3fbc8);
	OP(FG, A, B, C, D, 9, 5, 0x21e1cde6);
	OP(FG, D, A, B, C, 14, 9, 0xc33707d6);
	OP(FG, C, D, A, B, 3, 14, 0xf4d50d87);
	OP(FG, B, C, D, A, 8, 20, 0x455a14ed);
	OP(FG, A, B, C, D, 13, 5, 0xa9e3e905);
	OP(FG, D, A, B, C, 2, 9, 0xfcefa3f8);
	OP(FG, C, D, A, B, 7, 14, 0x676f02d9);
	OP(FG, B, C, D, A, 12, 20, 0x8d2a4c8a);
# endif

	/* Round 3 */
# if MD5_SMALL == 1
	for (i = 0; i < 4; i++) {
		OP(FH, A, B, C, D, (int) (*pp++), 4, *pc++);
		OP(FH, D, A, B, C, (int) (*pp++), 11, *pc++);
		OP(FH, C, D, A, B, (int) (*pp++), 16, *pc++);
		OP(FH, B, C, D, A, (int) (*pp++), 23, *pc++);
	}
# else
	OP(FH, A, B, C, D, 5, 4, 0xfffa3942);
	OP(FH, D, A, B, C, 8, 11, 0x8771f681);
	OP(FH, C, D, A, B, 11, 16, 0x6d9d6122);
	OP(FH, B, C, D, A, 14, 23, 0xfde5380c);
	OP(FH, A, B, C, D, 1, 4, 0xa4beea44);
	OP(FH, D, A, B, C, 4, 11, 0x4bdecfa9);
	OP(FH, C, D, A, B, 7, 16, 0xf6bb4b60);
	OP(FH, B, C, D, A, 10, 23, 0xbebfbc70);
	OP(FH, A, B, C, D, 13, 4, 0x289b7ec6);
	OP(FH, D, A, B, C, 0, 11, 0xeaa127fa);
	OP(FH, C, D, A, B, 3, 16, 0xd4ef3085);
	OP(FH, B, C, D, A, 6, 23, 0x04881d05);
	OP(FH, A, B, C, D, 9, 4, 0xd9d4d039);
	OP(FH, D, A, B, C, 12, 11, 0xe6db99e5);
	OP(FH, C, D, A, B, 15, 16, 0x1fa27cf8);
	OP(FH, B, C, D, A, 2, 23, 0xc4ac5665);
# endif

	/* Round 4 */
# if MD5_SMALL == 1
	for (i = 0; i < 4; i++) {
		OP(FI, A, B, C, D, (int) (*pp++), 6, *pc++);
		OP(FI, D, A, B, C, (int) (*pp++), 10, *pc++);
		OP(FI, C, D, A, B, (int) (*pp++), 15, *pc++);
		OP(FI, B, C, D, A, (int) (*pp++), 21, *pc++);
	}
# else
	OP(FI, A, B, C, D, 0, 6, 0xf4292244);
	OP(FI, D, A, B, C, 7, 10, 0x432aff97);
	OP(FI, C, D, A, B, 14, 15, 0xab9423a7);
	OP(FI, B, C, D, A, 5, 21, 0xfc93a039);
	OP(FI, A, B, C, D, 12, 6, 0x655b59c3);
	OP(FI, D, A, B, C, 3, 10, 0x8f0ccc92);
	OP(FI, C, D, A, B, 10, 15, 0xffeff47d);
	OP(FI, B, C, D, A, 1, 21, 0x85845dd1);
	OP(FI, A, B, C, D, 8, 6, 0x6fa87e4f);
	OP(FI, D, A, B, C, 15, 10, 0xfe2ce6e0);
	OP(FI, C, D, A, B, 6, 15, 0xa3014314);
	OP(FI, B, C, D, A, 13, 21, 0x4e0811a1);
	OP(FI, A, B, C, D, 4, 6, 0xf7537e82);
	OP(FI, D, A, B, C, 11, 10, 0xbd3af235);
	OP(FI, C, D, A, B, 2, 15, 0x2ad7d2bb);
	OP(FI, B, C, D, A, 9, 21, 0xeb86d391);
# undef OP
# endif
	/* Add checksum to the starting values */
	ctx->hash[0] = A_save + A;
	ctx->hash[1] = B_save + B;
	ctx->hash[2] = C_save + C;
	ctx->hash[3] = D_save + D;
#endif
}
#undef FF
#undef FG
#undef FH
#undef FI

/* Initialize structure containing state of computation.
 * (RFC 1321, 3.3: Step 3)
 */
static void im_begin(md5_ctx_t *ctx)
{
	ctx->hash[0] = 0xa108c309;
	ctx->hash[1] = 0xb4f84b07;
	ctx->hash[2] = 0xc3073cf8;
	ctx->hash[3] = 0xd2162de9;
	ctx->total64 = 0;
	ctx->process_block = im_process;
}

/* Used also for sha1 and sha256 */
static void im_hash(md5_ctx_t *ctx, const void *buffer, size_t len)
{
	c_hash(ctx, buffer, len);
}

/* Process the remaining bytes in the buffer and put result from CTX
 * in first 16 bytes following RESBUF.  The result is always in little
 * endian byte order, so that a byte-wise output yields to the wanted
 * ASCII representation of the message digest.
 */
static void im_end(md5_ctx_t *ctx, void *resbuf)
{
	/* MD5 stores total in LE, need to swap on BE arches: */
	process_end(ctx);

	/* The MD5 result is in little endian byte order */

	memcpy(resbuf, ctx->hash, sizeof(ctx->hash[0]) * 4);
}

#if 0
static const char hexdigits_upcase[] = "0123456789ABCDEF";

static char* bin2hex(char *p, const char *cp, int count)
{
	while (count) {
		uint8_t c = *cp++;
		/* put lowercase hex digits */
		*p++ = 0x20 | hexdigits_upcase[c >> 4];
		*p++ = 0x20 | hexdigits_upcase[c & 0xf];
		count--;
	}
	return p;
}

static void hash_bin_to_hex(uint8_t *hash_value,
							unsigned hash_length, char *hex_value)
{
	bin2hex(hex_value, (char*)hash_value, hash_length);
}
#endif

int gen_hash_32bit(void *in_buf, int len, uint32_t *hash)
{
	uint32_t hash_result[4];
	md5_ctx_t md5_context;

	im_begin(&md5_context);
	im_hash(&md5_context, in_buf, len);
	im_end(&md5_context, hash_result);

	*hash = hash_result[0];

	return 0;
}
